1. Field of the Invention
The present invention is in the field of aerospace fastener installation tooling, and it relates particularly to such tooling which is adapted for installation of Hi-Lok-type frangible threaded fasteners.
2. Description of the Prior Art
Hi-Lok-type aerospace fasteners are currently in widespread use throughout the aerospace industry. This type of fastener was developed by Hi-Shear Corporation of Torrance, Calif., and is manufactured under a variety of names, including Hi-Lok, Hi-Tigue, Hi-Light, Very Light, and others. The Hi-Lok-type frangible fastener is particularly adapted for fastening two or more metal panels or workpieces together where there is only limited access for installation tooling, as for example, in the fastening together of wing spar members.
The Hi-Lok-type frangible fastener includes two basic components, a pin or bolt component which has a head end and a threaded end, and a collar component which has an internally threaded body portion and a torque-off drive nut portion. Generally, a series of regularly spaced holes is bored through the panels which are preclamped in their final assembly relative positions. One of the most important features of this fastener is that it enables the fasteners to be installed with the installation tooling disposed on one side only of the panel assembly. However, the Hi-Lok-type fastener is not a blind fastener.
The pin or bolt component is inserted from the rear (relative to the tooling) of the panel assembly, the body of the collar component of the fastener is then preliminarily threaded a few turns onto the exposed threaded end of the pin or bolt component on the operational side of the panel assembly, and then the tooling is applied over the collar component on the operational side. This tooling includes a rotary socket member which has a forwardly opening hex recess that engages the torque-off drive nut portion of the collar component, and also a rotationally stationary hex key which fits into a broached hex cavity in the threaded end portion of the pin or bolt component of the fastener. The socket member is rotated, usually by an air-powered motor in the tool body, and threadedly runs the collar component of the fastener down onto the pin or bolt component until a design preload on the panels is reached, while at the same time the pin or bolt component of the fastener is held against rotation by the rotationally stationary hex key. At the design preload, the drive nut portion of the collar component is automatically torqued off of the threaded body of the collar component, which then becomes the nut portion of the fastener. Thus, another important advantage of the Hi-Lok-type fastener is that the design preload is always automatically accurately achieved without the need for manual monitoring. Avoidance of over-torquing is thus also automatically achieved. The Hi-Lok-type fastener has other advantages, including sealing applications in "wet wing" structures, and good aerodynamic characteristics.
The basic Hi-Lok fastener is disclosed in U.S. Pat. No. 2,940,495, issued Jun. 14, 1960 to George S. Wing, and assigned to Hi-Shear Rivet Tool Company of Torrance, Calif. The only tooling that patent discloses is a conventional Allen wrench and a socket head. No power tooling is disclosed.
Applicant is aware of the following six U.S. patents which disclose tooling suitable for the installation of Hi-Lok-type frangible fasteners. These are Batten U.S. Pat. No. 4,538,483, Batten U.S. Pat. No. 4,617,844, Zils U.S. Pat. No. 4,462,281, Bochman, Jr. U.S. Pat. No. 3,027,789, Bosten U.S. Pat. No. 3,584,527, and Bangerter et al. U.S. Pat. No. 3,323,394. The two Batten patents disclose essentially the same tooling, with a minor modification in the later one. The two Batten patents are the only ones of which applicant is aware which disclose what purports to be a quick-release and replacement system for removal of a damaged or broken hex key and replacement thereof in the ratchet drive head assembly of the tool. However, there are numerous problems associated with this key release and replacement system, which is a ball detent type of system, that are discussed in detail hereinafter.
The Zils patent discloses a straight drive type of tool wherein the socket and hex key approach the workpieces at right angles relative to the general plane of the workpieces. The Zils tool has the disadvantage that if the key is damaged or broken, disassembly of portions of the head assembly of the tool is required in order to remove and replace the hex key. It also has the disadvantage that the key may be difficult to remove because of sealant fouling, and a twisted hex key may not even be removable for replacement, or may damage the key holder, requiring almost complete disassembly of the tool head for removing the stuck key and its key holder. These disadvantages translate into substantial manual effort and tool down-time.
The Bochman patent discloses a geared L-head-type tool that might be applicable to a Hi-Lok-type frangible fastener, although there is no mention of a frangible fastener in this patent. Replacement of the key would require disassembly of a subhousing which houses an enlarged key head and key spring from the main tool head. This would require substantial manual effort and tool down-time.
The Bosten patent discloses a power tool which, by its nature, could be applied to a Hi-Lok-type frangible fastener, although its stationary key has a Phillips screwdriver-type head. It is a straight, offset drive which would require substantial disassembly, and hence manual effort and tool down-time, to remove and replace the bit or key. The Bangerter et al. patent is a straight drive power tool which is generally similar to the tools disclosed in both Bosten and Zils, but has a torque-limiting clutch associated with the bolt-restraining bar. As with both the Bosten and Zils devices, the Bangerter et al. device would require substantial disassembly to remove and replace a broken bar or key, requiring substantial effort and down-time. The binding problem discussed in connection with Zils would also be equally applicable to Bosten and Bangerter.